It is absolutely true that, when the favorable atmosphere is absent, the creativity of the artiste or the performer is not at its peak. This same thing happened in the case of Shankarji of the duo. Top associates like Jaikishan, Mukesh and Shailendra having gone for the heavenly abode, and a changed RK attitude and perspective to look at his ability must have hurt him in the heart and spirit.
What they call a decline is actually a state of non-performance of that artiste for want of favorable factors and an atmosphere in which he gave his previous bests!